playlist/registry: add option "as_directory"

This allows users to disable the "CUE files as directories" feature
without having to disable the CUE playlist plugin completely.  This
feature has been annoying some users.

7 files changed, 44 insertions, 2 deletions

diff --git a/NEWS b/NEWS
index a1b778d7e..7781f6e9a 100644
--- a/NEWS
+++ b/NEWS
@@ -6,6 +6,7 @@ ver 0.22.2 (2020/10/28)
   - qobuz/tidal: fix protocol errors due to newlines in error messages
   - smbclient: disable by default due to libsmbclient crash bug
 * playlist
+  - add option "as_directory", making CUE file expansion optional
   - soundcloud: fix protocol errors due to newlines in error messages
 * state_file: save on shutdown
 
diff --git a/doc/plugins.rst b/doc/plugins.rst
index 45a7b347f..06fe714c1 100644
--- a/doc/plugins.rst
+++ b/doc/plugins.rst
@@ -1231,6 +1231,8 @@ asx
 
 Reads :file:`.asx` playlist files.
 
+.. _cue_playlist:
+
 cue
 ---
 Reads :file:`.cue` files.
diff --git a/doc/user.rst b/doc/user.rst
index 06235c432..abd7c7b1f 100644
--- a/doc/user.rst
+++ b/doc/user.rst
@@ -500,6 +500,11 @@ The following table lists the playlist_plugin options valid for all plugins:
      - The name of the plugin
    * - **enabled yes|no**
      - Allows you to disable a playlist plugin without recompiling. By default, all plugins are enabled.
+   * - **as_directory yes|no**
+     - With this option, a playlist file of this type is parsed during
+       database update and converted to a virtual directory, allowing
+       MPD clients to access individual entries.  By default, this is
+       only enabled for the :ref:`cue plugin <cue_playlist>`.
 
 More information can be found in the :ref:`playlist_plugins`
 reference.
diff --git a/src/db/update/Playlist.cxx b/src/db/update/Playlist.cxx
index 03509522a..46286bb90 100644
--- a/src/db/update/Playlist.cxx
+++ b/src/db/update/Playlist.cxx
@@ -95,7 +95,7 @@ UpdateWalk::UpdatePlaylistFile(Directory &directory,
 	if (plugin == nullptr)
 		return false;
 
-	if (plugin->as_folder)
+	if (GetPlaylistPluginAsFolder(*plugin))
 		UpdatePlaylistFile(directory, name, info, *plugin);
 
 	PlaylistInfo pi(name, info.mtime);
diff --git a/src/db/update/SpecialDirectory.cxx b/src/db/update/SpecialDirectory.cxx
index 49c025d18..368bfb2db 100644
--- a/src/db/update/SpecialDirectory.cxx
+++ b/src/db/update/SpecialDirectory.cxx
@@ -52,7 +52,16 @@ static bool
 HavePlaylistPluginForFilename(const char *filename) noexcept
 {
 	const char *suffix = PathTraitsUTF8::GetFilenameSuffix(filename);
-	return suffix != nullptr && playlist_suffix_supported(suffix);
+	if (suffix == nullptr)
+		return false;
+
+	const auto plugin = FindPlaylistPluginBySuffix(suffix);
+	if (plugin == nullptr)
+		return false;
+
+	/* discard the special directory if the user disables the
+	   plugin's "as_directory" setting */
+	return GetPlaylistPluginAsFolder(*plugin);
 }
 
 bool
diff --git a/src/playlist/PlaylistRegistry.cxx b/src/playlist/PlaylistRegistry.cxx
index 5b7ef71d3..b9f6bb7ec 100644
--- a/src/playlist/PlaylistRegistry.cxx
+++ b/src/playlist/PlaylistRegistry.cxx
@@ -71,6 +71,9 @@ static constexpr unsigned n_playlist_plugins =
 /** which plugins have been initialized successfully? */
 static bool playlist_plugins_enabled[n_playlist_plugins];
 
+/** which plugins have the "as_folder" option enabled? */
+static bool playlist_plugins_as_folder[n_playlist_plugins];
+
 #define playlist_plugins_for_each_enabled(plugin) \
 	playlist_plugins_for_each(plugin) \
 		if (playlist_plugins_enabled[playlist_plugin_iterator - playlist_plugins])
@@ -96,6 +99,10 @@ playlist_list_global_init(const ConfigData &config)
 
 		playlist_plugins_enabled[i] =
 			playlist_plugin_init(playlist_plugins[i], *param);
+
+		playlist_plugins_as_folder[i] =
+			param->GetBlockValue("as_directory",
+					     playlist_plugins[i]->as_folder);
 	}
 }
 
@@ -106,6 +113,16 @@ playlist_list_global_finish() noexcept
 		playlist_plugin_finish(plugin);
 }
 
+bool
+GetPlaylistPluginAsFolder(const PlaylistPlugin &plugin) noexcept
+{
+	/* this loop has no end condition because it must finish when
+	   the plugin was found */
+	for (std::size_t i = 0;; ++i)
+		if (playlist_plugins[i] == &plugin)
+			return playlist_plugins_as_folder[i];
+}
+
 static std::unique_ptr<SongEnumerator>
 playlist_list_open_uri_scheme(const char *uri, Mutex &mutex,
 			      bool *tried)
diff --git a/src/playlist/PlaylistRegistry.hxx b/src/playlist/PlaylistRegistry.hxx
index 5e38ca23a..205fbb4b2 100644
--- a/src/playlist/PlaylistRegistry.hxx
+++ b/src/playlist/PlaylistRegistry.hxx
@@ -60,6 +60,14 @@ public:
 };
 
 /**
+ * Shall this playlists supported by this plugin be represented as
+ * directories in the database?
+ */
+gcc_const
+bool
+GetPlaylistPluginAsFolder(const PlaylistPlugin &plugin) noexcept;
+
+/**
  * Opens a playlist by its URI.
  */
 std::unique_ptr<SongEnumerator>